Resolve ignored_unit_patterns pedantic clippy lint in test suite

    warning: matching over `()` is more explicit
       --> tests/test.rs:950:22
        |
    950 |             mac!(let _: <Self as Trait>::Associated2;);
        |                      ^ help: use `()` instead of `_`: `()`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns
        = note: `-W clippy::ignored-unit-patterns` implied by `-W clippy::pedantic`

    warning: matching over `()` is more explicit
        --> tests/test.rs:1358:17
         |
    1358 |                 _ = async {
         |                 ^ help: use `()` instead of `_`: `()`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns

tests/test.rs

@@ -947,7 +947,7 @@ pub mod issue92 {
             mac!(let _ = <Self>::associated1(););
 
             // trait items
-            mac!(let _: <Self as Trait>::Associated2;);
+            mac!(let (): <Self as Trait>::Associated2;);
             mac!(Self::ASSOCIATED2;);
             mac!(<Self>::ASSOCIATED2;);
             mac!(<Self as Trait>::ASSOCIATED2;);
@@ -1355,7 +1355,7 @@ pub mod issue161 {
     impl Trait for MyStruct {
         async fn f(self: Arc<Self>) {
             futures::select! {
-                _ = async {
+                () = async {
                     println!("{}", self.0);
                 }.fuse() => {}
             }